Crossover tube construction

ABSTRACT

In a burner can for a combustion chamber for a gas turbine engine, a crossover tube interconnecting adjacent burner cans comprises a cylindrical outer wall extending laterally from a side opening in the burner can wall and a cylindrical inner wall radially spaced from the outer wall forming an annular passageway therebetween, the passageway having one end in communication with and terminating substantially at the combustion zone of the burner can. The outer wall has an opening for admitting cooling fluid into the annular passageway, whereupon cooling fluid entering the annular passageway is discharged from the annular passageway into the combustion zone and is carried downstream by currents within the combustion zone thereby cooling the downstream portion of the outer wall where it joins the side opening of the burner can wall. The invention described herein was made under or during the course of a contract with the Department of the Navy.

Calderon [111 3,811,274 [451 May 21,1974

[ 1 CROSSOVER TUBE CONSTRUCTION [75] Inventor: Henry A. Calderon, Newington,

Conn.

[73] Assignee: United Aircraft Corporation, East Hartford, Conn.

22 Filed: Aug.30, 1972 21 Appl. No.: 284,828

[52] US. Cl 60/3932, 60/3965, 60/3937 [51] Int. Cl. F0 2c 7/20 [58] Field of Search 60/39.32, 39.37, 39.65

[56] References Cited UNITED STATES PATENTS 3,001,366 9/1961 Shutts.. .L- 60/3937 2,979,898 4/1961 Ward 60/3937 2,722,803 11/1955 Travers 60/3965 2,611,243 9/1952 Huyton 60/3932 2,679,136 5/1954 Gaubatz 60/3932 3,439,498 4/1969 Melconian 60/3937 3,184,918 5/1965 Mulcahey 60/3937 Pr'imary Examiner-Carlton R. Croyle Assistant Examiner-Warren Olsen Attorney, Agent, or Firm-Stephen E. Revis 5 7] ABSTRACT In a burner can for a combustion chamber for a gas turbine engine, a crossover tube interconnecting adja-' cent burner cans comprises a cylindrical outer wall extending laterally from a side opening in the burner can wall and a cylindrical inner wall radially spaced from the outer wall forming an annular passageway therebetween, the passageway having one end in communication with and terminating substantially at the combustion zone of the burner can. The outer wall has an opening for admitting cooling fluidinto the annular passageway, whereupon cooling fluid entering the annular passageway is discharged from the annular passageway into the combustion zone and is carried downstream by currents within the combustion zone thereby cooling the downstream portion of the outer wall where it joins the side opening of the burner can wall.

The invention described herein was made under or during the course of a contract with the Department of the Navy.

1.1 Claims, 7 Drawing Figures PAIAYZI an I 3.811.274

saw 2 or 2 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to cross-over tubes for burner cans, and more particularly to an arrangement for cooling crossover tubes.

2. Description of the Prior Art As discussed in the U.S. Pat. to R. L. Mulcahey No. 3,184,918, crossover tubes are provided between adjacent burner cans (or flame tubes) to help equalize pressures within the cans and also to allow the flame from one can to pass into an adjacent burner can such that the igniting of one burner can may be used to ignite a series of interconnected cans, resulting in reducing the number of ignition devices required in an engine. As also noted in the Mulcahey patent, the crossover tubes interfere with the flow of air over the surface of the burner can with resultant overheating of the burner can and the crossover tube especially in the area of the downstream portion of the crossover tube where it joins with the burner can. The Mulcahey patent tries to cool this downstream area by providing a semicylindrical shield extending around the downstream portion of the crossover tube and in spaced relationship thereto for capturing air flowing past the crossover tube and directing it into the combustion zone of the burner can between an outwardly extending flange (on the downstream half of the crossover tube) and the wall of the burner can outwardly spaced from and adjacent the flange. However, as can be readily seen in FIG. 4 of the Mulcahey patent, the surface of the crossover tube flange facing toward the center of the burner can is directly exposed to hot gases of the combustion zone; with this arrangement it may not, under some circumstances, be possible to provide a sufficient flow of cooling fluid between the crossover tube and the semicylindrical sleeve to draw enough heat away from the flange to prevent damage to the flange.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved cooling arrangement for crossover tubes.

According to the present invention, a burner can comprises an annular side wall and a crossover tube extending laterally from a side opening in the side wall, the crossover tube, including an outer wall and an inner wall radially spaced forming an annular passageway therebetween, the end of the passageway furthest from the side wall being substantially blocked, and the end of the passageway nearest the side wall terminating substantially at the combustion zone of the burner can and being in gas communication with the combustion zone at least around the downstream portion of the passageway, the outer wall having an opening for admitting cooling fluid into the annular passageway. Cooling fluid entering the annular passageway is directed into the'combustion zone and is swept downstream by the flow of gases within the combustion zone forming a layer of cooling fluid along the internal surface of the side wall immediately downstream of the side opening; thislayer of cooling fluid acts as an effective shield between the side wall and the hot combustion gases.

The foregoing and other objects, features, and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a transverse sectional view through a semiannular combustion chamber showing the burner cans in elevation.

FIG. 2 is a view taken along the line 2-2 of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As an exemplary embodiment of the present invention, consider the semi-annular combustion chamber 10 of FIG.. 1 for use in a gas turbine engine. The combustion chamber 10 comprises inner and outer annular walls l2, 14 respectively, forming an annular flow path 16 therebetween. The combustion chamber 10 also includes a plurality of circumferentially spaced burner cans 18 disposed within the annular flow path 16. Each burner can 18 includes a substantially cylindrical side wall 20 extending. in a substantially upstreamdownstream direction, which in FIG. 1 is perpendicular to the plane of the drawing, the downstream direction being into the paper, and'a partially closed upstream end 22. Air exiting from the compressor section (not shown) of a gas turbine engine enters the upstream end of the annular flow path 16 of the combustion chamber 10; a portion of the air enters the burner cans 18 through openings 24 in the end 22. This air is mixed with fuel from fuel nozzles (not shown) positioned within a plurality of openings 26 in the end 22, whereupon the air and fuel is burned within the combustion along the line 3-3 zone 27 of the burner can 18, the combustion zone 27 being the space within the burner can 18 defined by the side wall 20 and the end 22. The remainder of the compressed air entering the annular flow path 16 travels downstream between and around the burner cans l8 and is used to help cool the side walls 20; some of this air also enters-the combustion zone 27 of the burner can 18 through a plurality of small holes 28 in the side wall 20 as can best be seen in FIGS. 2 and 3.

The combustion zones of adjacent burner cans 18 are kept in gas communication with each other through the use of crossover tubes. The crossover tube for the righthand burner can of FIG. 1 is designated by the numeral 30, and the crossover tube for the left burner can is designated by the numeral 32. Hereinafter in the specification and also in the claims following thespecification, the crossover tube end adjacent the side wall 20 is referred to as the proximal end of the crossover tube, and the crossover tube end furthest from the side wall 20 is referred to as the distal end of the crossover tube.

The crossover tube 30 comprises an outer wall 34 and an inner wall 36 radially spaced from and concentric to each other forming an annular passageway 38 therebetween. The outer wall 34 has a distal end 40 and taching the proximal end 42 of the outer wall 34 to the side wall by any suitable means such as by welding around the side opening 52 such as at 54 forming a welded joint. In this preferred embodiment the distal ends 40, .44 of the outer and inner walls 34, 36 respectively, are joined as shown in FIG. 3 thereby blocking off the distal end 48 of the annular passageway 38. The proximalend 46 of the inner wall 36 terminates substantially at the combustion zone 27 of the burner can 18,-thereby causing the proximal end 50 of the passageway 38 to end substantially at thecombustion zone; the main concern with the proximal end 46 of the inner wall 36 is that if it extends very far into the combustion zone 27, it may be burned off.

The outer wall 34 has an opening 56, the shape of which canbest be seen in FIG. 1, for admitting cooling air into thepassageway 38 Because the air is flowing downstream (to the left in FIG. 3) the opening 56 is judiciously located through that portion of the outer wall 34 which faces upstream. The air entering the passageway 38 through the opening 56 exits into the combustion zone 27 through the proximal end 50 of the passageway 38 that portion of the air which exits from the downstream portion of the passageway 38 is represented by the arrows 58, this air cools the proximal end of the outer wall 34 where it joins the side wall 20, which, ashas been stated, has been the main trouble spot for crossover tubes. As the air flows out of the passageway 38, it is carried downstream by currents within the combustion zone 27 and creates a protective shield of cool air between the combustion zone and the side wall portion 59 immediately adjacent and downstream of the crossover tube as is also indicated by the arrows 58."

In order to assure even and thorough cooling of all portions of the crossover tube 30 and the side wall portion 59, the opening 56 in this embodiment is in the form of an elongated slot, as best shown in FIG. 1; if we imagine a plane 60 perpendicular to the plane of the paper in F IG. 1 and containing the axis of the crossover tube '30, it can be seen that a portion of the slot 56' is located on one side of the plane and a portion'of the slot islocated on the other side such that air entering the slot 56 is'dist'ributed to'both that portion of the annular passageway 38 above'the plane 60 Iand that portion of the annular passageway 38-below the plane 60. The size ofthe slot 56 and its location and orientation with respect to the plane-60 can be chosen according to need; for example,as can be seen in FIG. I, because the axis of the crossover tube 30 is not perpendicular to the side wall 20, one side of vthe crossover 30 is longer than-the other; in orderthat the temperature of the air exiting from the annular passageway 38 into the combustion chamber is a fairly constant temperature 4 around the entire exit area of the passageway 38 the slot 56 has been angled so that it is parallel to the plane of the side opening .52; in this way air entering the annular passageway above the-plane 60 will travel approximately the same-distancetoget into the combustion zone as will .the air entering the slot..56below the plane 60, thus tending toresultin a similartemperature rise .for both volumes of air A feature of this invention which is best shown in FIG. 3, relates to air entering the holes 28 upstream of the crossover tube 30, which is the row of holes 28 to the right of the crossover tube 30 in FIG. 3. The proximal end 46 of the inner wall 36 extends past these holes such that the air entering the holes28 strikes the inner wall 36 as indicated by the arrow 61. Thus, were it not for the inner wall 36 acting as a barrier this air would rush across the side opening 52 and interfere with the proper functioning of the crossover tube.

A further detail in the construction of the crossover tube 30 is the plurality of circumferentially spaced dimples 62 in the inner wall 36 which serve to maintain concentricity between the inner wall 36 and the outer wall 34. In this embodiment four spherical dimples spaced 90 apart are utilized.

Also in this embodiment, a sleeve 64 is provided surrounding the distal end 40 of the outer wall 34; the sleeve fits closely around the outer wall 34 to minimize leakage, but is axially slidable with respect thereto. Sleeve 64 includes an outwardly extending flange 66, best shown in FIG. 3, for mounting to a cooperating crossover tube such as crossover tube 32 of an adjacent burner can. In this embodiment the sleeve 64 would be fixed with respect to the crossover tube 32. The sliding fitbetween the crossover tube 30 and the sleeve 64 accommodates a certain amount of relative motion between adjacent burner cans 18.

FIG. 4 shows an alternate embodiment of the invention. For ease of comparisomfeatures of FIG. 4 corresponding to features of FIG. 3 have the same reference numerals except they are primed. The basic difference between the embodiment shown in FIG. 3 and the embodiment shown in FIG. 4 is that the distal end 44 of the inner wall 36' is joined to the flange 66 rather than to the outer wall 34'. The sleeve 64' is still in axially slidable relationship to the outer wall 34. A further distinction between these two embodiments is in the opening through the outer wall 34".for admitting air into the annular passageway 38. As shown in FIGS. 5 and 6 two elongated slots 70 and 72 are provided, one each on either side of the plane 60. Each slot 70,.72 has an upstream edge 74, 76 respectively, and a downstream edge 78, 80 respectively; the downstream edges 78, 80 are bent radially outwardly to form upstream facing scoops for'capturing air flowing in a downstream direc tion, which would be toward the left in FIG. 5. As herein shown, the 'slots'70 and 72 are the same size; however, the size and shape and location of the slots can be chosen to achieve the desired flow of air within the annular passageway 38'.

FIG. 7 shows yet another embodiment of the present invention. This embodiment happens to be incorporated in the crossover tube 32 for, the left-hand burner can 18 of FIG. 1, and may be adapted to mate either with the embodiment shown in FIG. 3 or the embodiment shown in FIG. 4. For the purposes of clarity, features of the embodiment in FIG. 7 corresponding to features of the embodiments of FIGS. 3 and 4 are indicated by similar reference numerals which are double primed in FIG. 7. The basic distinction between the embodiment of FIG. 4 and the embodiment of FIG. 7 is the fact that the-sleeve (64' in FIG. 4) has been removed and a radially outwardly extending flange 82 has been added to the distal end 40" of the outer wall 34".,

The flanges 66" and 82 mate with each other and are fastened together by any suitable means such as by rivets (not shown). The embodiment of FIG. 7 also differs from the embodiment of FIG. 4 in that the opening 56", similar to the opening 56 of the embodiment of FIG. 3, is utilized rather than the pair of slots 70, 72 shown in FIG. 5. It should be noted, however, that the slots 70, 72 could just as easily have been utilized in the embodiment of FIG. 7. It can readily be seen that the flange 66 of FIG. 4, or the flange 66 of FIG. 3 can be designed to mate with the flange 66" of FIG. 7 such that the flanges can be fastened together by some suitable means to form a pair of cooperating crossover tubes between adjacent burner cans such as the cooperating crossover tubes 30, 32 shown in FIG. 1.

Although this invention has been described with respect to preferredembodiments, it should be understood by those skilled in the art that various other changes and omissions in the form and detail thereof may be made therein without departing from the spirit and the scope of the invention.

Having thus described typical embodiments of my invention, that which I claim as new and desire to secure by Letters Patent of the United States is:

l. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway.

2. The burner can according to claim 1 wherein said side opening has a downstream edge, and said side wall has an inner surface extending downstream of said side opening. said outer wall including a downstream facing portion. the proximal end of said downstream facing portion joining said downstream edge forming a joint, said annular passageway being adapted to direct a layer of cooling fluid over'said joint and over the inner surface of said side wall directly downstream of said side opening.

3. The burner can according to claim 1' wherein said outer wall includes an upstream facing portion and said opening in said outer wall is in said upstream facing portion.

4. The burner can according to claim 3 wherein first crossover tube is intersected by a plane extending in an upstream-downstream direction, said plane containing the axis of said crossover tube, and said opening is an elongated slot including a portion on one side of said plane and a portion on the other side of said plane, wherein a cooling fluid entering said annular passageway through said elongated slot is distributed to the portions of said annular passageway on both sides of said plane.

5. The burner can according to claim 1 wherein said outer wall includes two of said openings, one of said openings being located on one side of a plane that exstream edge, said can also including a substantially cy-' tends in an upstream-downstream direction and contains the axis of said crossover tube, the other of said openings being located on the other side of said plane, each of said openings being an elongated slot extending in a substantially axial direction and having an upstream edge and a downstream edge, said downstream edge being bent outwardly away from said axis to form an upstream facing scoop. I

6. A burner can for a combustion chamber, said ca including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said side wall including a plurality of holes immediately upstream and adjacent said first crossover tube for admitting cooling fluid into said combustion zone, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including an upstream facing portion having an opening therein'for admitting cooling fluid into said annular passageway, the proximal end of said inner wall extending past said side wall and acting as a barrier to said cooling fluid entering said combustion zone through said holes for preventing said fluid from flowing directly across said side opening and interfering with the proper functioning of said crossover tube.

7. The burner can according to claim 6 wherein said innerwall includes a plurality of outwardly extending dimples of a height approximately equal to the radial height of said annular passageway for maintaining concentricity between said inner wall and said outer wall.

8. The burner can according to claim 2 wherein the distal end of said outer wall and the distal end of said inner wall are joined.

9. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein and having an inner surface extending downstream of said side opening, said side opening including a downlindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossovertube mounted in a side opening of an adjacent burner can, said firstcrossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith,

said outer wall including a downstream facing portion,

the proximal end of said downstream facing portion,

joining said downstream edge forming a joint, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway, said annular passageway being adapted to direct a layer of said cooling fluid over said joint and over the inner surface of said side wall directly downstream of said side opening, said crossover tube also comprising a cylindricalsleeve closely surrounding'the distal end of said outer wall and in axially slidable relationship thereto, the distal end of said inner wall being joined to said sleeve and also including means adapted for attachment to the crossover tube of the adjacent burner can.

10. A burner can for a combustion chamber, said can includinga substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, saidside wall having at least one side opening therein and having an inner surface extending downstream of said side opening, said can also including a substantially cylindrical first crossover tube having an axis, said crossover. tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including a downstream facing portion, the proximal end of said downstream facing portion joining said downstream edge forming a joint, ,said outer wall having at least one opening therein for admitting cooling fluid into said: annular passageway, said annular passageway being adapted to direct a layer of said cooling fluid'over said joint and over the inner surface of said side wall directly downstream of said side opening, said crossover tube also comprising a cylindrical sleeve closely surrounding the distal end of said outer wall and in axially slidable relationship thereto, the distal end of said outer wall being joined to the distal end of said inner wall, said sleeve including means adaptedfor attachment to the crossover tube of the adjacent burner can.

1 l. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein and having an inner surface extending downstream of said side opening, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including a downstream facing portion, the proximal end of said downstream facing portion joining said downstream edge forming a joint, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway, said annular passageway being adapted to direct a layer of said cooling fluid over said joint and over the inner surface of said side wall directly downstream of said side opening, the distal end of said outer wall including a radially outwardly extending flange, and the distal end of said inner wall including a radially outwardly extending flange inabutting relationship to said outer wall flange, said flanges being adapted to mate with the crossovertube of the adjacent burner can. t I 

1. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway.
 2. The burner can according to claim 1 wherein said side opening has a downstream edge, and said side wall has an inner surface extending downstream of said side opening, said outer wall including a downstream facing portion, the proximal end of said downstream facing portion joining said downstream edge forming a joint, said annular passageway being adapted to direct a layer of cooling fluid over said joint and over the inner surface of said side wall directly downstream of said side opening.
 3. The burner can according to claim 1 wherein said outer wall includes an upstream facing portion and said opening in said outer wall is in said upstream facing portion.
 4. The burner can according to claim 3 wherein first crossover tube is intersected by a plane extending in an upstream-downstream direction, said plane containing the axis of said crossover tube, and said opening is an elongated slot including a portion on one side of said plane and a portion on the other side of said plane, wherein a cooling fluid entering said annular passageway through said elongated slot is distributed to the portions of said annular passageway on both sides of said plane.
 5. The burner can according to claim 1 wherein said outer wall includes two of said openings, one of said openings being located on one side of a plane that extends in an upstream-downstream direction and contains the axis of said crossover tube, the other of said openings being located on the other side of said plane, each of said openings being an elongated slot extending in a substantially axial direction and having an upstream edge and a downstream edge, said downstream edge being bent outwardly away from said axis to form an upstream facing scoop.
 6. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said side wall including a plurality of holes immediately upstream and adjacent said first crossover tube for admitting cooling fluid into said combustion zone, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said pasSageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including an upstream facing portion having an opening therein for admitting cooling fluid into said annular passageway, the proximal end of said inner wall extending past said side wall and acting as a barrier to said cooling fluid entering said combustion zone through said holes for preventing said fluid from flowing directly across said side opening and interfering with the proper functioning of said crossover tube.
 7. The burner can according to claim 6 wherein said inner wall includes a plurality of outwardly extending dimples of a height approximately equal to the radial height of said annular passageway for maintaining concentricity between said inner wall and said outer wall.
 8. The burner can according to claim 2 wherein the distal end of said outer wall and the distal end of said inner wall are joined.
 9. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein and having an inner surface extending downstream of said side opening, said side opening including a downstream edge, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including a downstream facing portion, the proximal end of said downstream facing portion joining said downstream edge forming a joint, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway, said annular passageway being adapted to direct a layer of said cooling fluid over said joint and over the inner surface of said side wall directly downstream of said side opening, said crossover tube also comprising a cylindrical sleeve closely surrounding the distal end of said outer wall and in axially slidable relationship thereto, the distal end of said inner wall being joined to said sleeve and also including means adapted for attachment to the crossover tube of the adjacent burner can.
 10. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein and having an inner surface extending downstream of said side opening, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including a downstream facing portion, the proximal end of said downstream facing portion joining said downstream edge forming a joint, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway, said annular passageway being adapted to direct a layer of said cooling fluid over said joint and over the inner surface of said side wall directly downstream of said side opeNing, said crossover tube also comprising a cylindrical sleeve closely surrounding the distal end of said outer wall and in axially slidable relationship thereto, the distal end of said outer wall being joined to the distal end of said inner wall, said sleeve including means adapted for attachment to the crossover tube of the adjacent burner can.
 11. A burner can for a combustion chamber, said can including a substantially cylindrical side wall and a partially closed upstream end defining a combustion zone, said side wall having at least one side opening therein and having an inner surface extending downstream of said side opening, said can also including a substantially cylindrical first crossover tube having an axis, said crossover tube mounted in said side opening and extending outwardly from said side wall and adapted to mate with a second crossover tube mounted in a side opening of an adjacent burner can, said first crossover tube having a distal end and a proximal end and comprising inner and outer radially spaced walls forming an annular passageway therebetween, the distal end of said passageway being substantially closed, the proximal end of said passageway terminating substantially at said combustion zone and being in gas communication therewith, said outer wall including a downstream facing portion, the proximal end of said downstream facing portion joining said downstream edge forming a joint, said outer wall having at least one opening therein for admitting cooling fluid into said annular passageway, said annular passageway being adapted to direct a layer of said cooling fluid over said joint and over the inner surface of said side wall directly downstream of said side opening, the distal end of said outer wall including a radially outwardly extending flange, and the distal end of said inner wall including a radially outwardly extending flange in abutting relationship to said outer wall flange, said flanges being adapted to mate with the crossover tube of the adjacent burner can. 